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Artificial Ground Freezing

Artificial Ground Freezing

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Artificial Ground Freezing

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  1. Artificial Ground Freezing Will Greenwood Clark Green Mike Partenio CEE 542

  2. Contents 1.0 Introduction 2.0 Effects on Soil and Properties 3.0 In the Field 4.0 Advantages and Disadvantages 5.0 Case Study 6.0 Current State (Info from SoilFreeze, Inc.) 7.0 Conclusions

  3. 1.0 Introduction 1.1 History 1.2 Concept 1.3 Classification Refrigeration plant (MoreTrench)

  4. 1.1 History

  5. 1.2 Concept Wagner and Yarmak 2012 Johanssan 2009

  6. 1.2 Concept MoreTrench

  7. 1.3 Classification • ASTM D4083-89

  8. 2.0 Effects on Soil Properties 2.1 Hydraulic Conductivity 2.2 Strength and Stiffness 2.3 Volume Change Characteristics 2.4 Laboratory Testing

  9. 2.1 Hydraulic Conductivity • Frozen ground practically impermeable • Be aware of field limitations • Hydraulic conductivity may increase after thawing • Concern when freezing into bedrock

  10. 2.2 Strength and Stiffness • Strength increases • Typical strengths of frozen soils (Klein 2012) • Sand: 15 MPa • Clay: 3 MPa • Frozen sands and frozen clays exhibit similar stress-strain behavior • Stiffness increases

  11. 2.2 Strength and Stiffness Da Re et al. 2003

  12. 2.3 Volume Change • Pore water volume increase of 9% • Soil heave • Clays may consolidate below freezing front • Thaw settlement

  13. 2.4 Laboratory Testing • Lab testing standards are documented by both ASTM and JGS • ASTM D7300-11 – Strength of frozen soil samples under constant strain rate • ASTM D5520-11 – Creep properties of frozen soil samples by uniaxial compression • JGS 0171-2003 – Frost heave prediction in soils • Thermal properties always tested

  14. 2.4 Laboratory Testing • Mostly intended for natural ground freezing • Standards for triaxial testing of unfrozen soil do not apply to frozen soil • Shear stress, triaxial compression, thaw settlement standards still needed

  15. 3.0 In the Field 3.1 Equipment 3.2 Methods for Design 3.3 Freezing Time 3.4 Special Considerations

  16. 3.1 Equipment • Mobile Freeze Plant • Freeze Pipes • Steel • HDPE • Coolant • Typically Calcium Chloride. • Commercial coolants. MoreTrench

  17. 3.1 Equipment MoreTrench Wagner and Yarmak 2012

  18. 3.2 Methods for Design • Performance approach with contractor. Experience needed. • Sanger and • Sayles 1979, Harris 1995 • FEM • TEMP/W • Plaxis Geo-Slope International McCain et al. 2013

  19. 3.3 Freezing Time Jessberger and Vyalov 1978 Sanger and Sayles 1979

  20. 3.4 Special Considerations • Groundwater velocity (< 2 m/day threshold) (Klein 2012). • Smaller spacing or multiple pipe rows. • LN2 • Reduce hydraulic conductivity. • Groundwater salinity • Reduces freezing temperature and strength. • Incomplete freezing.

  21. 3.4 Special Considerations • Temperature monitoring • Thermocouples in key locations. • Soil heave and creep. • Monitor closely – be aware of adjacent structures.

  22. 4.0 Advantages • Soil applicability and versatility • All soil and site conditions • Various improvement geometries • Angled freeze pipes • Cost-effective • Replaces multiple methods • Ground returns to original state Freeze pipe geometry for cross passage construction, Nanjing Metro, China Dayong, Hui(2010)

  23. 4.0 Disadvantages • Energy intensive • Extensive monitoring • Possible failures • Uncontrolled frozen ground thickness • Damage to AGF equipment, causing leaks • Damage to nearby structures

  24. 5.0 Case Study Dijk, P. and Bouwmeester-van den Bos, J. (2001)

  25. 6.0 Current Conditions • Ground freezing is becoming increasingly more common for everyday shoring projects • Currently competitive on a cost-basis • Typical cost approximately $30 – $60 per square foot of frozen soil wall area (SoilFreeze, Inc.)

  26. 7.0 Conclusions • Freeze soil pore water with coolant circulation through pipes to: • Control groundwater or contaminant mobility • Increase strength and stiffness • Versatile and technique for ground improvement • Applicable to entire soil range • Applicable to various site stratigraphy and conditions • Proper site characterization is key

  27. Questions?

  28. References http://www.geoengineer.org/education/web-based-class-projects/select-topics-in-ground-improvement/ground-freezing?showall=&start=8